Epidemiological studies have shown a prevalence of patellar tendinopathy (jumper's knee) of 40- 50% among high-level volleyball players. This clinical condition is characterized by exercise-related pain in the quadriceps insertion at the upper patellar pool or at the lower patellar pool and the patellar ligament. Patellar tendinopathy is often found in sports where athletes are required to perform jumping actions or rapid accelerations, thereby placing high demands on the knee extensor apparatus. Our understanding of the causes of partial tendon ruptures of the patellar tendon is incomplete. Training volume and the floor surface are extrinsic factors, which correlate positively with the prevalence of jumper's knee. Data on intrinsic factors are conflicting, and mostly related to static biomechanical parameters. In a recent case-control study, we evaluated some dynamic characteristics of the leg extensor apparatus, and the results suggest that players with jumper's knee perform better on jump tests than healthy controls, especially tests involving eccentric work. The purpose of the present study was to examine the leg extensor characteristics in a larger cohort of players using a more comprehensive jump and strength testing program. To study the dynamic characteristics of the extensor apparatus the players performed a test program consisted of a standing jump, a countermovement jump, a 15-second rebound jump test, a standing jump with a 20-kg load, and a standing jump with a load corresponding to one-half of the subjects body weight.
The study was carried out during an international volleyball tournament in Oslo, Norway. The six Norwegian teams that participated in the men's elite class in the tournament were invited to take part in the study. These were amateur teams which otherwise compete in the top division of the Norwegian Volleyball Federation leagues. The teams consisted of 53 players, and 47 of these (87%) consented to take part in an interview, clinical examination, and a series of standardized jump and power tests. Of the 47 players participating in the study, 24 players (51.0%) were clinically diagnosed with current jumper's knee affecting at least one side. Twenty players (42.6%) had never experienced problems from any knee, whereas three players reported having had previous knee problems identified as jumper's knee (6.4%). Players with jumper's knee had a significantly higher body weight (presumably due to greater muscle mass than the controls, and they trained more with weights. When using a 'composite jump index' that combined the results from all the jump tests done, the players with jumpers knee performed significantly better than the control group. This finding indicates that higher demands on the extensor apparatus among players with jumpers knee results in an increased risk of patellar ligament overuse.